The present disclosure relates, in various exemplary embodiments, to polymer nanocomposites prepared by forming metal nanoparticles in-situ in a polymer melt in an extruder. Methods for making the nanoparticles, as well as articles formed therefrom, are also disclosed.
Nanocomposites are particle-filled polymers for which at least one of the dimensions of the dispersed particles is in the nanometer (10−9 meter) or nanoscale range (typically from about 1 to about 200 nanometers). Nanocomposites often have superior physical and mechanical properties over their microcomposite counterparts, such as improved modulus, reduced gas permeability, flame retardance, and improved scratch resistance. Moreover, the nanoscale dispersion of the particles within the polymer frequently does not produce the brittleness and opacity typically found in microcomposites or larger sized particles.
Nanocomposites may be made from ex-situ melt blending processes. However, in conventional melt blending processes, relatively uniform dispersion of nanoparticles within the polymer, such as a polycarbonate matrix, is difficult to achieve. Typically, the nanoparticles remain largely localized in the form of agglomerates in the polymer matrix.
Additionally, some nanoparticle generation processes require intermediate temperature or time conditions for optimum sized particles. However, melt blending can be incompatible with such processes.
Nanoparticles may also be generated from metal salt solutions. Unfortunately, conventional melt blending processes can restrict the volume of solvent which can be added, thus restricting nanoparticle formation. Commercial scale solvent usage and disposal can also present serious hazards, and stripping of the solvent during the blending process increases the likelihood of particle agglomeration or oxidation to an undesired state.
When metal or metal oxide particles are added as external additives to polymers via melt or solution blending, their particle size and shape cannot be controlled. The particles also tend to agglomerate together.
Sometimes, higher levels of nanoparticles can be added to the polymer matrix to increase a desired property. However, this use of higher levels may also increase the desired property to the detriment of other properties. For example, higher levels can result in a nanocomposite having inferior optical properties, such as reduced transparency or increased haze.
There remains a need for nanocomposites, and methods for producing the same, that overcome dispersion issues arising from conventional melt blending processes.